Photovoltaic module for roofs

ABSTRACT

A photovoltaic module generates electrical power when installed on a roof. The module is constructed as a laminated sandwich having a transparent protective upper layer adhered to a photovoltaic layer. The photovoltaic layer is adhered to a rigid layer formed from a fiber reinforced plastic. The laminated sandwich has a frame around the perimeter. The laminated panel has a layer of double stick tape on the bottom to adhere the panel to the surface of a roof.

RELATED APPLICATIONS

The present application is a continuation-in-part application of U.S.patent application Ser. No. 11/615,934, filed on Dec. 22, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to solar panels for generating electricalenergy and more particularly relates to photovoltaic modules integratedinto a laminated, weather resistant sandwich for installation on flatroofs.

2. Description of the Related Art

Conventional photovoltaic panels for generating electrical power forresidences and businesses are flat and are placed on a portion of a roofthat is exposed to the sun. Historically, such panels were placed onstructures erected on the roof to support and protect the panels. Morerecently, photovoltaic panels have become available that can be mounteddirectly on a flat roof. See, for example, US Patent ApplicationPublication No. 2005/0178248 A1 to Laaly et al., which discloses a panelthat incorporates a roofing membrane into the panel structure. The panelis intended to be installed on a new roof or replacement roof with themembrane providing moisture protection for the underlying structure aswell as providing electrical power. Although generally suitable forroofing applications, the additional membrane adds unnecessarymanufacturing costs and requires additional steps to install on a roof.

SUMMARY OF THE INVENTION

The photovoltaic panel described herein and illustrated in the attacheddrawings enables the electricity-generating solar panel to be installedon an existing flat roof directly over an existing roof. The panel isformed in the size and shape of conventional 4-foot by 8-foot panelsthat are easily mounted using tape or other suitable adhesive systems.The panel does not include a membrane, and is easier to manufacture andinstall.

In accordance with aspects of a preferred embodiment of the invention, aphotovoltaic panel comprises a lower rigid substrate, a middlephotovoltaic layer having electrical output connectors, and an uppertransparent protective layer. The layers are formed into a laminatedsandwich with the layers fixed to each other by a heat-activated,transparent adhesive, such as, for example, ethylene-vinyl-acetate(EVA). The layers and coating of EVA act as binders and cushions for thelayers of the laminated photovoltaic panel. Other suitable adhesives,such as, for example, polyvinylbuterol (PVB), or another pottantmaterial that acts as a binder and cushion can be substituted for theEVA.

The middle photovoltaic layer comprises a plurality of electricallyinterconnected photovoltaic cells. For example, the middle photovoltaiclayer advantageously comprises 160 photovoltaic cells arranged in anarray of rows and columns.

The upper transparent upper layer preferably comprises a suitablethickness of waterproof, chemically resistant resin, such as, forexample, fluorinated ethylene propylene (FEP) resin. Such a resin iscommercially available from E.I du Pont de Nemurs and Company as DuPont™Teflon® FEP film. The FEP film is a transparent, thermoplastic film thatcan be heat sealed, thermoformed, vacuum formed, heat bonded, or thelike to produce the transparent upper layer. In preferred embodiments,the upper transparent layer is softened during a curing process to allowa portion of the transparent layer to form a protective layer along thesides of the laminated structure.

The photovoltaic panel further includes an outer frame that surroundsthe outer edges of the laminated sandwich. Preferably, the outer frameis secured to the laminated sandwich by a silicon adhesive or othersuitable waterproof adhesive. In preferred embodiments, the bottom ofthe rigid substrate is secured to the existing roof by a layer ofdouble-stick tape, such as, for example, a self-sealing tape having aformulation of resins, thermoplastics and non-curing rubbers. A suitabledouble-stick tape is marketed by Eternabond, Inc., of Hawthorn Woods,Ill., USA, as Eternabond™ Double Stick™.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain aspects in accordance with embodiments of the present inventionare described below in connection with the accompanying drawing figuresin which:

FIG. 1 illustrates a perspective view of an exemplary embodiment of alaminated photovoltaic panel;

FIG. 2 illustrates an enlarged cross-sectional view of the photovoltaicpanel of FIG. 1 taken along the lines 2-2 in FIG. 1; and

FIG. 3 illustrates an exploded perspective view of the photovoltaicpanel of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in FIGS. 1, 2 and 3, a laminated photovoltaic panel 100is configured as a generally rectangular panel, which is sized andshaped in accordance with the sizes and shapes of conventional buildingmaterials. Thus, the panel 100 can be handled by a construction crewwithout requiring any special material handling equipment. The panel 100is assembled in a factory or other suitable environment so that thepanel 100 is complete and ready to install on a flat roof or otherlocation having adequate exposure to the sun. In the illustratedembodiment, the panel 100 has dimensions of approximately 96 inches (8feet) by 48 inches (4 feet) and has a thickness of less thanapproximately 0.2 inch when installed. Thus, the panel 100 does not addsignificant height to a roof structure. Although not intended to be usedas a walking surface, the panel 100 has sufficient structural integrityto support the weight of a construction worker or a roofing inspectorand to resist the impact of objects dropped on the panel 100.

The panel 100 has a transparent upper protective layer 110 that facesupward and is exposed to the sun. A middle layer 120 is positionedbeneath the upper protective layer 110. The middle layer 120 comprises aplurality of photovoltaic cells 122 electrically interconnected to forman photovoltaic array. The middle layer 120 rests on a rigid lower layer130. The middle layer 120 is secured to the rigid lower layer 130 by alower adhesive layer 140. The middle layer 120 is secured to the upperprotective layer 110 by an upper adhesive layer 150. The middle layer120 is thus encapsulated between the lower adhesive layer 140 and theupper adhesive layer 150.

The upper protective layer 110 provides impact protection as well asweather protection to the panel 100. The upper protective layer 110advantageously comprises DuPont™ Teflon® fluorinated ethylene propylene(FEP) resin, which is formed into a film layer of suitable thickness(e.g., approximately 0.1 inch). Thus, the photovoltaic cells 122 in themiddle layer 120 are exposed to direct sunlight without being exposed tomoisture and other climatic conditions and without being exposed todirect impact by feet, falling objects, and debris. Tempered glasshaving a suitable thickness may also be used as the upper protectivelayer 110.

In the illustrated embodiment, the rigid lower layer 130 comprises fiberreinforced plastic (FRP). For example, the FRP layer advantageouslycomprises a polyester resin with embedded stranded glass fibers. In oneadvantageous embodiment, the FRP layer has a thickness of approximately0.079 inch. The rigid lower layer of FRP provides an advantageouscombination of rigidity, light weight, very low permeability, andflatness.

Preferably, the lower adhesive layer 140 is provided as a thin film thatis positioned on the upper surface of the rigid lower layer 130. Thearray of photovoltaic cells 122 in the middle layer 120 is thenpositioned on the lower adhesive layer 140. In the illustratedembodiment, the lower adhesive layer 140 advantageously comprises atransparent adhesive, such as, for example, ethylene-vinyl-acetate(EVA). EVA is a transparent, heat-activated adhesive that isparticularly suitable for securing the cells. Other suitable adhesives,such as, for example, polyvinylbuterol (PVB), or other pottantmaterials, can be substituted for the EVA.

After positioning the array of photovoltaic cells 122 on the loweradhesive layer 140, the upper transparent adhesive layer 150 is placedover the middle layer 120 so that the photovoltaic cells 122 aresandwiched between the two transparent adhesive layers. The upperadhesive layer 150 should match the physical characteristics of thelower adhesive layer. In the illustrated embodiment, both the upperadhesive layer 150 and the lower adhesive layer 140 comprise EVA, butother suitable transparent adhesives can be substituted for the EVA. Thetransparent upper protective layer 110 is then positioned over the uppertransparent adhesive layer 150 to complete the laminated structure shownin an enlarged partial cross section in FIG. 2.

The EVA material and the use of the EVA material to bind the layers of alaminated photovoltaic cell are described, for example, in U.S. Pat. No.4,499,658 to Lewis. In addition to acting as a binder to secure thephotovoltaic cells 122 between the upper protective layer 110 and thelower rigid layer 130, the upper EVA layer 150 and the lower EVA layer140 also act as a cushion between the two outer layers.

The photovoltaic cells 122 are electrically interconnected in aseries-parallel configuration in a conventional manner to provide asuitable output voltage. For example, in the illustrated embodiment, 160photovoltaic cells 122 are arranged in 9 rows of 18 cells each; however,the two cells are omitted from the uppermost row to provide room forpositioning a junction box 170 having a first weather-resistantelectrical conductor 172 and a second weather-resistant electricalconductor 174. As shown in FIG. 3, the photovoltaic panel 100 includestwo panel output conductors 176, 178 that extend from the top surface ofthe middle layer 120 in the area of the omitted photovoltaic cells. Eachof the panel output conductors 176, 178 is connected to a respective oneof the weather-resistant electrical conductors 172, 174 within thejunction box 170 after the photovoltaic panel 100 is laminated, asdiscussed below.

The upper protective layer 110, the middle layer 120, the lower layer160, and the two adhesive layers 140 and 150 are stacked in the ordershown in FIGS. 2 and 3 and are aligned to form the sandwich structureshown in FIGS. 1, 2 and 3. The free end of each of the panel outputconductors 176, 178 are covered with a temporary covering (e.g., a clothtube, or the like) during the lamination process. The structure ispermanently laminated in a known manner using heat and pressure. In oneadvantageous embodiment, the structure is laminated in a vacuumlaminator in the manner described, for example, in US Patent ApplicationPublication No. 2005/0178248 A1 to Laaly et al. In particular, thestructure is first subjected to a vacuum to remove any trapped gasbubbles in the EVA adhesives. The structure is then subjected to highpressure to force the layers together as tightly as practical. Thestructure is then heated to a suitable temperature (e.g., approximately160° C.) to cure the adhesives in the layers 140 and 150 and therebypermanently bond the adjacent layers.

The laminated structure is held at the high temperature for a sufficienttime to cure the upper transparent adhesive layer 150 and the lowertransparent adhesive layer 140 and to cause the two transparent adhesivelayers to adhere together to become a combined layer that completelyencapsulates the photovoltaic cells 122. The high temperature alsocauses the upper transparent layer 110 to soften and flow to provide theprotective upper coating described above. The laminated structure isthen allowed to cool to ambient temperature.

Although the resulting laminated structure is moisture resistant and issufficiently strong to withstand the flexing that may occur duringordinary handling of the panel 100 during normal conditions, anadditional structural element is added in the preferred embodiment inorder to improve the moisture resistance and the structural stability.In particular, the panel 100 further includes a weather-resistantplastic frame shown in FIG. 3. In a preferred embodiment, the framecomprises a first frame half 180 and a second frame half 182. The framehalves are positioned around the edges of the laminated structure asshown in the cross-sectional view in FIG. 2 for the first frame half180. The exposed ends of the two frame halves are butted together toform a complete frame around the perimeter of the panel 100. Althoughshown as two separate frame halves, it should be understood that asingle length of frame material can also be used by bending the materialaround the edges of the panel 100 and butting the two free ends.

As further illustrated in FIG. 2, the frame halves 180, 182 preferablycomprise a plastic extrusion with a U-shaped cross section having a wallthickness of approximately 0.05 inch. For example, the plastic materialadvantageously comprises polyvinylchloride (PVC), thermoplasticpolyolefin (TPO) or another suitable material. In the illustratedembodiment, the two parallel legs of the U-shaped extrusion have lengthsof approximately 0.1875 inch measured from the inside of the base of theextrusion. The width of the base of the U-shaped extrusion is selectedto accommodate the thickness of the laminated layers of the panel 100.In the illustrated embodiment, the inside width of the base is selectedto be approximately 0.18 inch.

In the illustrated embodiment, each frame half 180, 182 surroundsapproximately one-half of the outer perimeter of the panel 100. Asfurther shown in FIG. 2, each frame half is secured to the outside edgeof each layer and to a portion of the upper surface of the upper layer110 and a portion of the lower surface of the rigid lower layer 130 by alayer 190 of a suitable adhesive. For example, in one embodiment, theadhesive layer 190 advantageously comprises a silicon adhesive, which issufficiently strong to permanently fix the frame halves 180, 182 to thepanel 100. After positioning the frame halves on the panel 100, the endsof the frame half 180 may be secured to the respective ends of the framehalf 182 by gluing or another suitable method if desired. As discussedabove, if a single length of frame material is used, the two ends of theframe may be connected at a single location.

After the lamination process is completed and the two frame halves 180,182 are secured to the edges of the panel 100, the junction box 170 issecured to the upper layer 110 in a conventional manner (e.g., usingsilicon adhesive). As the junction box 170 is installed, the two paneloutput conductors 176, 178 extending from the photovoltaic layer 120 arepassed through a hole (not shown) in the bottom of the junction box 170.The temporary coverings over the two panel output conductors 176, 178are removed, and the two panel output conductors 176, 178 areelectrically connected within the junction box 170 to the twoweather-resistant external conductors 172, 174 using conventionalinterconnection devices. A removable top of the junction box 170 is thensecured over the conductor interconnection devices to provide aweather-resistant seal.

As shown in FIGS. 2 and 3, the preferred method of installation of thepanel 100 comprises applying a layer 200 of tape to the bottom surfaceof the rigid lower layer 130. Preferably, the tape layer 200 comprises asuitable double-stick tape, such as, for example, a self-sealing tapehaving a formulation of resins, thermoplastics and non-curing rubbers. Asuitable self-sealing double-stick tape is marketed by Eternabond, Inc.,of Hawthorn Woods, Ill., USA, as Eternabond™ Double Stick™. Thedouble-stick tape is adhesive on both sides. When manufactured, thedouble-stick tape has a release layer on each side to prevent adhesion.One release layer is advantageously removed during the process ofmanufacturing the panels. The exposed adhesion side of the tape layer200 is positioned on and adhered to the bottom surface of the rigidlower layer 130 before shipping the panel 100. Then, during installationof the panel 100, the remaining release layer is removed so that thepanel can be adhered to the surface of an existing roof. The surface ofthe existing roof is cleaned and suitably prepared to receive the panel100. After installation, suitable pressure is applied to the upper layer110 of the panel 100 to permanently adhere the panel to the surface ofthe roof. In FIG. 2, the tape layer 200 is illustrated as comprising aplurality of narrow strips of tape (e.g., 4-inch widths). The tape canalso be obtained in wider widths to improve the manufacturing process.

The present invention is disclosed herein in terms of a preferredembodiment thereof, which provides an exterior building panel as definedin the appended claims. Various changes, modifications, and alterationsin the teachings of the present invention may be contemplated by thoseskilled in the art without departing from the intended spirit and scopeof the appended claims. It is intended that the present inventionencompass such changes and modifications.

1. A photovoltaic module, comprising: an upper transparent layercomprising fluorinated ethylene propylene resin; a photovoltaic layerpositioned beneath the upper transparent layer, the photovoltaic layercomprising a plurality of electrically interconnected photovoltaic cellsand an electrical output connector; a first layer of heat-activatedtransparent adhesive interposed between the upper transparent layer andthe photovoltaic layer to adhere the photovoltaic layer to the uppertransparent layer; a rigid layer positioned beneath the photovoltaiclayer; a second layer of heat-activated transparent adhesive interposedbetween the photovoltaic layer and the rigid layer to adhere thephotovoltaic layer to the rigid layer; a frame having an upper portionand a lower portion, the frame positioned to hold edges of the uppertransparent layer, the photovoltaic layer and the rigid layer betweenthe upper portion and the lower portion; and an adhesion layer having afirst surface attached to an exposed lower surface of the rigid layerand having a second surface for adhering the module to a roofingsurface.
 2. The photovoltaic module of claim 1, wherein the rigid layercomprises a fiber reinforced plastic.
 3. The photovoltaic module ofclaim 1, wherein the adhesion layer comprises tape having a firstadhesion side and a second adhesive side, the first adhesion side fixedto the lower surface of the rigid layer, the second adhesion side havinga releasable cover, the releasable cover being removable to adhere theadhesion layer to the lower surface of the rigid layer, thereby fixingthe photovoltaic panel to a roof surface.
 4. The photovoltaic module ofclaim 1, wherein heat-activated transparent adhesive comprisesethylene-vinyl-acetate.